1. Field of the Invention
The invention generally relates to motion-restraining devices and more particularly to an improved motion-restraining device for dissipating at a controlled rate the force of a body moving unidirectionally, such as the spring-loaded mass as the mass is deployed from an operational spacecraft.
As can readily be appreciated by those familiar with the aerospace industry, it often is desirable to provide aboard spacecraft booms and truss-like structures adapted to be collapsed into a launch configuration and thereafter extended into a deployed configuration, for deploying science payloads, once the spacecraft becomes operational. In order to achieve this result, it has been suggested that collapsible, spring-loaded booms be provided. Of course, release of the spring-loaded booms without restraint tends to apply turning moments to the spacecraft from which the boom is extended. Such moments can, in operation, exceed the control capabilities of attitude control systems provided therefor so that serious navigational problems are thus introduced. It is therefore desirable to deploy the booms at relatively slow rates in order to dissipate the released energy over relatively long periods of time.
2. Description of the Prior Art
Among the devices heretofore employed for purposes of dissipating the energy of moving bodies, at controlled rates, are those which utilize escapement mechanisms such as those often employed in the field of horology. Such mechanisms commonly utilize an escape wheel and a two-arm pallet which dissipate energy by converting it into heat at the impact of the pallet with the escape wheel. However, it has been found that such devices simply are not suitable for use in controlling the deployment of spring-loaded booms from operational spacecraft. For example, in order to accommodate swing clearance for the impact members of a two-arm pallet either a relatively small radius on the escape wheel or a small radius on each arm of the pallet must be provided. Because of this design requirement, essentially line contact can be expected to occur between the impacting surfaces with an attendant brinelling at the point of impact. This result can, of course, result in malfunction of the escapement mechanism with attendant abortion of the spacecraft's mission.
While it has been suggested that brinelling can be obviated either by changing the slope of the escape teeth or by employing harder materials, it is apparent that a greater slope tends to decrease the decelerating force undesirably. Moreover, the coefficient of restitution of harder materials would tend to return energy to the system, instead of dissipating it. Additionally, escapement geometry of the prior art devices limits oscillation of a pallet to approximately 5.degree. which requires either that a high oscillation frequency be provided or that a high inertia flywheel be utilized or both. Furthermore, tangential shock is introduced into the driving gear system of conventional escapement devices at each tooth engagement.
In view of the foregoing, it should be apparent that there exists a need for an improved motion-restraining device adapted to be employed aboard operative spacecraft for purposes of controlling the rates at which spring-loaded booms are deployed. It is therefore the general purpose of the instant invention to provide a motion-restraining device for use aboard spacecraft which overcomes the aforementioned difficulties and disadvantages without impairing the advantages achievable through the use of actuating devices for extending collapsible booms and truss-like structures.